This invention relates to fluids and methods used in treating a wellbore penetrating a subterranean formation. In particular, this invention refers to methods for well clean-out applications using recyclable viscosity fluids containing a sphingan heteropolysaccharide.
In wellbore cleanout operations, the objective is removal of wellbore fill material, such as sand, scale or organic materials, and other debris, from the wellbore. Many reservoirs produce some sand or fines that may not be carried to surface in the produced fluid. Accumulations of fill material may eventually increase in concentration within the lower wellbore, possibly restricting production. Cleanouts using coiled tubing, snubbing or hydraulic workover techniques are performed routinely to remove wellbore fill. The term wellbore cleanout is also known as well workover and intervention.
A typical wellbore cleanout operation involves preparing at the surface of a wellsite conventional polymer based viscous fluid of density adequate to reach the bottom of the wellbore, and injecting the fluid into the wellbore. A port of the fluid is then returned to the surface by circulation, to remove wellbore fill material. Due to exposure to the extreme wellbore conditions, as well as degradation due to techniques for removal of the wellbore fill material, the fluid generally loses viscous properties required further cleanout treatments, and must either be discarded, or mixed with fresh fluid, in order to reuse the fluid.
Therefore, the need exists for wellbore cleanout methods which overcome the necessity to either discard at least a portion of cleanout fluid after a single treatment or significant replenishment with fresh fluid. A method that can achieve the above would be highly desirable, and the need is met at least in part by the following invention.